Ditto. An outlet tester is the place to start. Get one that tests the usual and fault interruption. Trigger and test the fault interruptors with the onboard test switches too.

You will want a simple voltage tester for switches, light and ceiling fan connections, etc. too.

If you get into this, you will find many uses for a multi-tester and learning to use one can save you some money in doing preliminary diagnoses prior to bringing in an electrician. THERE IS NO SUBSTITUTE FOR A QUALIFIED ELECTRICIAN THOUGH! When in doubt, or most times even when you are absolutely sure, call one. They are much cheaper than house fires.

Your eyes, goof. If you can not tell visually if something is amiss, then next step is the tester, or vice versa. I never trust the testers, because they can not tell you if there is a "bootlegged" ground, without actually taking the cover plate off the outlets.